In a subsequent statement to CNBC, the Justice Department reiterated that explanation, adding that Sessions "met hundreds—if not thousands—of foreign dignitaries and their staff."

"In filling out the SF-86 form, the Attorney General's staff consulted with those familiar with the process, as well as the FBI investigator handling the background check, and was instructed not to list meetings with foreign dignitaries and their staff connected with his Senate activities," Ian Prior, deputy director of public affairs at the Justice Department, said in a statement.

The FBI declined to comment to CNN.

The revelation renews scrutiny on the meeting between Sessions and Kislyak. In the attorney general's confirmation hearing, Sen. Al Franken, D-Minn., asked what Sessions would do if he learned that someone in the Trump staff had communicated with the Kremlin during the campaign.

Sessions replied, "I have been called a surrogate at a time or two in that campaign, and I did not have communications with the Russians, and I'm unable to comment on it."

While Democrats allege that Sessions misled the Senate Judiciary Committee with that remark, Flores disagreed. She argued that the question was about meetings that took place in his capacity as a surrogate for the campaign, not for those which happened in his capacity as a member of the Armed Services Committee.